To maintain forward and backward compatibility its important to add or remove a field that has some default value.
In case of Avro, You can only use null as a default value if it is one of the branches of the union.
Changing the datatype of a field is possible, provided that Avro can convert the type
Changing a field name is very tricky. reader’s schema can contain aliases for field names, so it can match an old writer’s schema field names against the aliases
So, Changing a field name is (possibly) backward compatible but not forward compatible.
The simplest solution is to include a version number at the beginning of every encoded record, and to keep a list of schema versions in your database
A database of schema versions is a useful thing to have.
Dataflow Through Databases
Dataflow Through Services: REST and RPC
Message-Passing Dataflow
message brokers are used as follows: one process sends a message to a named queue or topic, and the broker ensures that the message is delivered to one or more consumers of or subscribers to that queue or topic
There can be many producers and many consumers on the same topic.
Message brokers typically don’t enforce any particular data model a message is just a sequence of bytes with some metadata
Distributed actor frameworks
The actor model is a programming model for concurrency in a single process
logic is encapsulated in actors. Each actor typically represents one client or entity, it may have some local state, and it communicates with other actors by sending and receiving asynchronous messages.
Summery
Databases, where the process writing to the database encodes the data and the
process reading from the database decodes it
RPC and REST APIs, where the client encodes a request, the server decodes the
request and encodes a response, and the client finally decodes the response
Asynchronous message passing (using message brokers or actors), where nodes
communicate by sending each other messages that are encoded by the sender
and decoded by the recipient
with a bit of care, backward/forward compatibility and rolling upgrades are quite achievable
